Acoustic position locating systems known in the prior art include a variety of ultrasonic signal generating means. Some systems employ a pointer having an incorporated spark gap. The spark gap generates an acoustic signal which is propagated to orthogonally oriented, linear microphones. Other systems employ acoustic transducers which emit periodic, acoustic signals that are received by appropriately located microphones. Circuitry measures the propagation time of the acoustic signal between the emitter and the respective receivers, with the propagation times being converted into distances to enable the location of the transmitter. One example of the latter type of ultrasonic position locating system can be found in U.S. Pat. Ser. No. 07/412,885 now U.S. Pat. No. 4,991,148 filed Sept. 26, 1989 to the inventor hereof.
In such systems, it is important that the signal transmitted by the acoustic transducer be of a limited duration. An acoustic signal having a long "tail" or other continuing signal characteristic will cause various reflections to occur which are difficult to accommodate in the receiving circuitry. One prior art technique used to achieve such limited duration acoustic signals has been to provide mechanical dampening for the ultrasonic transducer that causes the signal to be foreshortened. The problem with such mechanical damping is that, in addition to shortening the signal, it also decreases the signal amplitude of the initially generated acoustic wave.
The application of a pulsatile signal to an acoustic transducer causes ultrasonic oscillations thereof on both the leading and lagging edges of the pulse. This occurs because the acoustic transducer is responsive to a step function voltage to produce an acoustic output, irrespective of the direction of transition of the energizing signal. The transducers response to the lagging edge of the pulse signal extends the time duration of the generated acoustic signal and results in an undesirably long signal waveform.
Accordingly, it is an object of this invention to provide a circuit for driving an acoustic transducer that enables the transducer to provide an optimum duration output signal.
It is another object of this invention to provide an improved circuit for driving an acoustic transducer which makes use of circuitry already present in the system to improve the quality of a transducer's output signal waveform.